1. Technical Field
The present invention relates to image forming apparatuses which are for forming an image.
2. Related Art
Image forming apparatuses such as a laser beam printer have been well-known. Such image forming apparatuses are furnished with, for example, an image bearing body that is for bearing dot-like latent images, and a rotatable developer bearing roller that is for making visible as a developer image, using developer borne on a surface thereof, the dot-like latent images borne by the image bearing body. The image bearing body is rotatable about a central axis, and the developer bearing roller is opposes the image bearing body such that an axial direction thereof is parallel to an axial direction of the image bearing body.
When the image forming apparatus receives image signals, etc. from external devices such as host computers, it positions a developing device at a developing position which is opposite to the image bearing body, and forms a toner image by developing, using toner particles in the developing device, a latent image borne by the image bearing body. The image forming apparatus transfers the toner image onto a medium, and finally forms an image on the medium.
Some of the above-mentioned developer bearing rollers have, on a surface thereof, a helical groove portion which has a predetermined inclination with respect to an axial direction of the developer bearing roller and which is formed having a uniform pitch in the axial direction. When dot-like latent images are made visible as a developer image by the developer which is borne by the developer bearing roller having the groove portion, there are cases in which unevenness in density may occur periodically in the developer image (for example, unevenness in density which is caused because an amount of the developer borne by the groove portion is more than an amount of the developer borne by any other section than the groove portion).
Further, if dot-like latent images are respectively borne by a plurality of divided regions which are arranged in rows along a direction which intersect, at a predetermined intersection angle, an axial direction of the central axis of the image bearing body (hereinafter also referred to as an intersection direction), a plurality of the dot-like latent images that are borne are formed along the intersection direction.
Under such a circumstance, depending on a relative position of each of a plurality of the divided regions with respect to the groove portion, unevenness in density caused by the groove portion may become conspicuous in the developer image which has been made visible. For example, when the image bearing body and the developer bearing roller rotate in order to make dot-like latent images visible as a developer image, if the relative position of each of a plurality of divided regions with respect to the groove portion is the same, each dot-like latent image borne by each of a plurality of the divided regions may be made visible, as a developer image, by the developer borne on a same area of the groove portion. This may make unevenness in density caused by the groove portion conspicuous in the developer image which has been made visible.
Besides, image forming apparatuses such as a laser beam printer are furnished with, for example, a rotatable image bearing body that is for bearing dot-like latent images in divided regions which are divided into lattices, and a rotatable developer bearing roller that bears the developer on a surface thereof and is for making visible, as a developer image, the dot-like latent images borne by the image bearing body. When the image forming apparatus receives image signals, etc. from external devices such as host computers, it positions a developing device at a developing position which is opposite to the image bearing body, and forms a toner image by developing, using the developer in the developing device, a latent image borne by the image bearing body. The image forming apparatus transfers the toner image onto a medium, and finally forms an image on the medium. Besides, the above-mentioned developer bearing roller is furnished with a depressed and projecting section on the surface thereof, in order to bear the developer.
However, if the depressed/projecting section is formed on the surface of the developer bearing roller, when dot-like latent images are made visible as a developer image, there are cases in which unevenness in density caused by the depressed and projecting section may occur periodically in the developer image (for example, unevenness in density which is caused because an amount of developer borne by a projecting portion is different from an amount of developer borne by a depressed portion). Thus, unevenness in density occurring periodically is conspicuous, so that image quality may deteriorate.
Note that JP-A-1-102486 and JP-A-2000-228728 are examples of a related art.